feat(deacon): improve timing and add heartbeat command

Timing changes for more relaxed poke intervals:
- Daemon heartbeat: 60s → 5 minutes
- Backoff base: 60s → 5 minutes
- Backoff max: 10m → 30 minutes
- Fresh threshold: <2min → <5min
- Stale threshold: 2-5min → 5-15min
- Very stale threshold: >5min → >15min

New command:
- `gt deacon heartbeat [action]` - Touch heartbeat file easily

Template rewrite:
- Clearer wake/sleep model
- Documents wake sources (daemon poke, mail, timer callbacks)
- Simpler rounds with `gt deacon heartbeat` instead of bash echo
- Mentions plugins as optional maintenance tasks
- Explains timer callbacks pattern

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/daemon/daemon_test.go

@@ -12,8 +12,8 @@ func TestDefaultConfig(t *testing.T) {
 	townRoot := "/tmp/test-town"
 	config := DefaultConfig(townRoot)
 
-	if config.HeartbeatInterval != 60*time.Second {
-		t.Errorf("expected HeartbeatInterval 60s, got %v", config.HeartbeatInterval)
+	if config.HeartbeatInterval != 5*time.Minute {
+		t.Errorf("expected HeartbeatInterval 5m, got %v", config.HeartbeatInterval)
 	}
 	if config.TownRoot != townRoot {
 		t.Errorf("expected TownRoot %q, got %q", townRoot, config.TownRoot)